You’ll need to download and install this deb: http://cache.saurik.com/debs/odcctools_286-8_iphoneos-arm.deb
This is the original Darwin’s CC tools from Saurik’s archive.
If you don’t know how to install .deb files:
1. Install Filza from Cydia.
2. Open the link above.
3. There should be an option to open the .deb file in Filza. Hitting that will open Filza and you should see the file.
4. Open the file and hit install button which should be in the top left. Install it and then respring.
You’ll be able to install Cracktool3 now.